So it got clarified that, rather than using Extra Rin’s body, Ereshkigal and Ishtar are both using Rin’s body, and her hair turns blonde when Ereshkigal is in control because that’s the “proper” appearance for a goddess.
It was also explained that Tiamat can corrupt and control Servants, similar to what Dark Sakura does in Heaven’s Feel
And with Babylonia completed, the final battle was released and cleared within 3 days. As far noteworthy reveals…
As for where Grand Order goes from here, who knows, besides that they’ve mentioned another Valentine’s event. But as one person pointed out, even at the end of the “final” battle, Mashu is still only at NP level 3 out of 5.